Down Syndrome Facts

Medically reviewed by Michael Crescione on July 5, 2017Written by Kimberly Holland on July 5, 2017

Overview

During a baby’s development, chromosomes form and cells divide rapidly and in a particular order. Sometimes, however, this symphony of chromosome creation goes awry. When that happens, disorders and diseases can occur.

In the case of Down syndrome, extra chromosomes can lead to the telltale symptoms of the developmental and intellectual disorder. The signs and symptoms of this extra genetic material are distinctive. People with Down syndrome develop recognizable facial features. They also have developmental disorders and intellectual difficulties.

Here are a few facts and statistics about Down syndrome to help you know a bit more about this common condition.

Facts and statistics

People with Down syndrome have an extra chromosome.

The nucleus of a typical cell contains 23 pairs of chromosomes, or 46 total chromosomes. Each of these chromosomes determines something about you, from your hair color to your sex. People with Down syndrome have an extra copy or partial copy of chromosome 21.

Each year, 6,000 babies are born with Down syndrome in the United States.

One out of every 700 babies born in the United States have the condition. That makes Down syndrome the most common chromosomal birth defect.

Symptoms of Down syndrome aren’t the same for each person.

The genetic disorder causes many distinct characteristics, like a small stature, upwardly slanting eyes, a flattened bridge of the nose, and a short neck. However, each person will have different degrees of the characteristics, and some of the features may not appear at all.

Three different types of Down syndrome exist.

While the condition may be thought of as a singular syndrome, three different types exist. Trisomy 21, or nondisjunction, is the most common. It accounts for 95 percent of all cases. The other two types are called translocation and mosaicism. Regardless of which type a person has, everyone with Down syndrome has an extra part of chromosome 21.

Maternal age is the only known risk factor for Down syndrome.

Eighty percent of children with either trisomy 21 or mosaicism Down syndrome are born to moms who are younger than 35 years old. Younger women have babies more frequently, so the number of babies with Down syndrome are higher in that group.

However, moms who are older than 35 are more likely to have a baby affected by the condition. The older a woman is when she becomes pregnant, the higher the chances are that she’ll have a baby with the condition.

Down syndrome is a genetic condition, but it’s not hereditary.

Neither trisomy 21 nor mosaicism is inherited from a parent. These cases of Down syndrome are the result of a random cell division event during the baby’s development.

But one-third of translocation cases are hereditary. That means the genetic material that can lead to Down syndrome is passed from parent to child. This portion of translocation cases accounts for 1 percent of all Down syndrome cases.

Mothers who carry the gene for translocation are more likely to pass it to their child.

Both parents can be carriers of the translocation Down syndrome genes, but the risk of having a second child with this type of the condition is about 10 to 15 percent if the mother carries the genes. If the father is the carrier, the risk is about 3 percent.

The average age of survival continues to increase.

At the turn of the 20th century, children with Down syndrome rarely lived past age 9 years. Now, thanks to advancements in treatment, the majority of people with the condition will live to age 60. Some may live even longer.

People with Down syndrome can have other medical issues.

Many children born with the condition have no other serious birth defects, but some will. The most common is hearing loss. Three-quarters of people with Down syndrome have hearing difficulties. Obstructive sleep apnea affects 50 to 75 percent of people with Down syndrome, and as many as half of all people with Down syndrome are also born with heart defects.

Babies who are also born with a congenital heart defect are more likely to die in the first year of life.

Infants born with Down syndrome who also have a heart defect at birth are nearly five times more likely to die before their first birthday. Likewise, a congenital heart defect is one of the greatest predictors of death before age 20. However, new developments in heart surgery are helping people with the condition live longer.

The number of infants born with Down syndrome who die before their first birthday is falling.

From 1979 to 2003, the rate of death for a person born with Down syndrome during their first year of life fell by about 41 percent. That means about five percent of babies born with Down syndrome will die by age 1 year.

Half of older adults with Down syndrome will develop memory loss.

People with Down syndrome are living to be much older, but as they get older, it’s not uncommon for them to develop thinking and memory problems. These signs and symptoms often begin showing around age 50. People with Down syndrome may first show signs of Alzheimer’s disease in their fifties and sixties.

Early intervention is vital.

While Down syndrome can’t be cured, treatment and teaching life skills can go a long way to improve the child’s — and eventually the adult’s — quality of life. Treatment programs often include physical, speech, and occupational therapies, life skills classes, and educational opportunities. Many schools and foundations offer highly specialized classes and programs for children and adults with Down syndrome.

Babies of every race can have Down syndrome.

Down syndrome does not occur in one race more than another. Unfortunately, however, black infants born with the condition are less likely to survive beyond infancy. The reasons why are not clear.

Women who have had one child with Down syndrome have an increased chance of having another child with the condition.

If a woman has one child with the condition, her risk for having a second child with the syndrome are about 1 in 100. The chances of a woman having a baby with Down syndrome increase throughout the woman’s life, especially after age 35.

Takeaway

Down syndrome remains the most common chromosomal disorder children are born with in the United States today, but the future is getting brighter for them. As treatments and therapies improve, lifespans are increasing, and people with Down syndrome are prospering. Greater understanding of complications and preventative measures are helping caregivers, educators, and doctors anticipate and plan for a longer future.

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